Some interesting info from WW

It’s clear that creating a caloric deficit is the only way to lose weight, but how do vegetarian diets rank compared to other diets when it comes to weight loss? Further, is there typically a difference in weight between vegetarians and non-vegetarians?
A review of the scientific literature on the subject found that 29 out of 40 studies reported that vegetarians weighed significantly less than non-vegetarians. This was observed in both males and females, and various ethnic groups.1 Although vegetarians tend to have healthier lifestyle habits that may influence weight, e.g., more exercise and less smoking, some studies were performed within a population with similar lifestyles, and the differences in weight were still seen.Vegetarian diets and weight statusThe type of vegetarian diet can also impact weight status. Results from a study of 37,875 healthy men and women participating in the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford) found that after adjusting for age, mean BMI was significantly highest among meat-eaters (24.41 kg/m2 in men, 23.52 kg/m2 in women) and lowest in the vegans (22.49 kg/m2 in men, 21.98 kg/m2 in women). Vegetarians and fish eaters had comparable mean BMI in between the other groups.1
Further, vegetarians have a lower rate of overweight and obesity. Data analyzed in 55,459 healthy women that participated in the Swedish Mammography Cohort revealed a 40 percent prevalence of overweight and obesity among omnivorous women, 29 percent among semi-vegetarians and vegans, and 25 percent among lacto-ovo vegetarians.2
Because vegetarian diets are associated with lower body weight, rate of overweight and obesity, vegetarians may also have a lower risk of certain diseases like heart disease and diabetes.
Vegetarian diets and weight lossTaking in fewer calories than your body needs, by either decreasing caloric intake through your diet and/or expending energy through exercise, is the only way to lose weight. One strategy that can be used to reduce caloric intake is to follow a vegetarian diet.
Research shows that following a vegetarian diet can result in, but does not guarantee successful weight loss. For example, results from a study published in January 2008 found that sedentary and overweight adults assigned to follow a lacto-ovo vegetarian diet lost an average of 7.9 percent of their body weight after 18 months. However, participants who followed a standard diet also lost 8 percent of their body weight.3 The insignificant difference in weight loss between those following a standard vs. vegetarian diet shows that it is not the type of diet that controls weight loss, but rather the caloric deficit.
Another study showed that overweight, postmenopausal women who were assigned to a low-fat, vegan diet lost 12.76 pounds (+/- 7.04 pounds) compared to 8.36 pounds (+/- 6.16 pounds) lost by those following a control diet based on National Cholesterol Education Program guidelines.4 The higher weight loss seen with the low-fat, vegan diet may be attributed to its low energy density. Research has shown that incorporating low energy density foods as part of a diet can lead to greater weight loss. (For more information on energy density, read the Science Center library article, Cutting Calories: Portion Control, Energy Density).
The Weight Watchers Approach:Any type of vegetarian diet can be incorporated into the Weight Watchers plan. However, to ensure all nutritional needs are met, some specific guidelines are provided.